1. Field of the Invention
The present invention relates to liquid crystal display devices, and more particularly to a liquid crystal display device and a method of fabricating the same in which a single common line parallel to a gate line is formed at the center of a substrate, which may result in enhanced transmittance.
2. Discussion of the Related Art
Demands for display devices are gradually increasing with development of the information age. Correspondingly, a variety of flat panel display devices, such as a Liquid Crystal Display (LCD), Plasma Display Panel (PDP), Electro Luminescent Display (ELD), and Vacuum Fluorescent Display (VFD) devices, for example, have recently been studied and utilized as display devices in various equipment.
Among the aforementioned display devices, liquid crystal display devices currently have replaced Cathode Ray Tubes (CRTs) and been used as portable image display devices, owing to advantageous characteristics and advantages, such as high resolution, slim design, low weight and low power consumption. In addition to the purpose of portable appliances, such as monitors of laptop computers, liquid crystal display devices have been developed in various ways as monitors of computers and televisions that receive and display broadcast signals.
Such a liquid crystal display device includes a lower substrate on which a thin film transistor array is formed, an upper substrate on which a color filter array is formed, and a liquid crystal layer formed between the lower substrate and the upper substrate. Additionally formed on the lower substrate are a plurality of unit pixels defined by gate lines and data lines orthogonally intersecting each other, a plurality of pixel electrodes formed at the respective unit pixels to which data signals are individually applied, and thin film transistors to individually drive the pixel electrodes. Also, additionally formed on the upper substrate are color filters formed on a per unit pixel basis, a black matrix to prevent leakage of light, and column spacers to attain a gap between the upper substrate and the lower substrate.
Representative driving modes that have been used in the aforementioned liquid crystal display devices include, for example, a Twisted Nematic (TN) mode in which orientation of a liquid crystal director is twisted by 90 degrees and thereafter voltage is applied to control the liquid crystal director, and an In-Plane Switching (IPS) mode in which liquid crystals are driven by a horizontal electric field between pixel electrodes and common electrodes which are arranged in parallel on the same substrate.
In particular, in the in-plane switching mode, the pixel electrodes and the common electrodes are alternately formed on a lower substrate such that liquid crystals are oriented by a transversal electric field created between the pixel electrodes and the common electrodes. Although IPS mode liquid crystal display devices are beneficial to achieve a wider viewing angle, the IPS mode liquid crystal display devices have a low aperture ratio and transmittance. To solve this problem, Fringe Field Switching (FFS) mode liquid crystal display devices have been proposed.
In the case of FFS mode liquid crystal display devices, a plurality of pixel electrodes in the form of slits may be formed on a unitary common electrode, or a plurality of common electrodes in the form of slits may be formed on a unitary pixel electrode, whereby liquid crystal molecules are driven by a fringe field created between the pixel electrode(s) and the common electrode(s).
Hereinafter, a conventional liquid crystal display device will be described with reference to the accompanying drawings.
FIG. 1A is a plan view illustrating a conventional liquid crystal display device, and FIG. 1B is an enlarged plan view of a unit pixel of FIG. 1A, illustrating a fringe field switching mode liquid crystal display device.
Referring to FIGS. 1A and 1B, the conventional liquid crystal display device includes a plurality of gate lines GL and data lines DL that orthogonally intersect each other to define unit pixels on a substrate, and Thin Film Transistors (TFTs) formed at intersections of the gate lines GL and the data lines DL. In particular, the conventional liquid crystal display device further includes common lines CL provided equal in number to the gate lines GL and arranged parallel to the gate lines GL.
The TFT includes a gate electrode 10, source and drain electrodes 15a and 15b, and a semiconductor layer (not shown). The liquid crystal display device is a fringe field switching mode liquid crystal display device in which a fringe field is created by a unitary common electrode 30 and a plurality of pixel electrodes 20 in the form of slits with an insulating film interposed therebetween.
In this case, the pixel electrode 20 is connected to the drain electrode 15b through a drain contact hole 20a, and the common electrode 30 is connected to the common line CL through a common contact hole 30a. The above described conventional liquid crystal display device, however, is reduced in aperture ratio by an area of the common line CL in each unit pixel because the common lines CL are provided equal in number to the gate lines GL. In particular, a high-resolution display device has a less area of each unit pixel than a low-resolution display device, and therefore an area of the common line CL on a per unit pixel basis may be increased in the high-resolution display device than in the low-resolution display device, which causes a considerable reduction in transmittance.